1) Measurements of signal levels in amplifier input/s (antenna output/s). The measurements can be done with e.g. TM 3000 R10502 signal level meter. The aim is to determine whether the levels are sufficient for further processing, i.e. amplifying and distributing the signals to ensure the intended signal levels in all subscriber outlets (Table 2). If needed, preamplifiers should be used.

3) Choice of the type of distribution network is determined by accessibility to ducts, power supplying etc, but first of all - the concept of distribution (e.g. program packages).

4) In accordance with the chosen type of the network we have to create its diagram. In a network based on branches and taps, each story is equipped with a tap characterized by adequate through and tap-off attenuation (taking into consideration differences in signal levels due to different lengths of the cables). In the case of a network based on distribution of signal from one central point, all taps are situated in this point. The staircases are linked with a splitter, with use of additional amplifiers if needed (for larger number of subscribers in staircases - then it is two-stage system). Location of the splitter should ensure the same or very similar distances to all subscribers.

5) Calculations of attenuation L between building amplifier and subscriber outlets. The calculations will allow to find minimum attenuation Lmin (usually in the outlet closest to the amplifier) and maximum attenuation Lmax (usually in the farthest outlet). If Lmin and Lmax do not meet recommendations, the design has to be revised.

6) To the L value we add Uabmin level and 3 dB safety margin that allows for connecting two receivers, having required Uba level in amplifier output.

7) The maximum output level Ubamax of the amplifier is determined by adding to Uba the allowance for reduction of intermodulation distortions (Table 1), and 3 dB margin, which makes it possible to increase the number of distributed programs in the future (up to two times).

8) The last stage is adjustment of the set of channel amplifiers to equalize levels of all programs.

within one amplifier section from point A to point B (the amplifier and all dissipative elements to the next amplifier or receiver) the effective amplification factor should be 0 dB , i.e. the amplifier only compensates the attenuation in the section, (L dB - A dB = 0)

Illustration of amplifier section

due to attenuation of coaxial cable increasing with frequency, the amplifiers used should ensure adequate correction;

it is needed to calculate effective signal-to-noise ratio of the network and compare it with S/Nmin value - correctly designed MATV systems with one amplifier ensure that the ratio is only slightly larger than that of a typical TV set, which means imperceptible changes of image and sound quality

it is not recommended to use splitters for distribution of signal among larger number of receivers - lack of proper matching within the whole frequency spectrum and interferences injected to the network by the receivers (heterodynes) cause interferences that deteriorate reception quality; taps ensure better separation among subscriber outlets, which practically eliminates these problems

FM radio channels are considered as one channel and the calculations only take into consideration the strongest signal

it is not recommended to use band amplifiers at the input of the installation - they also amplify unwanted signals

each program should be received by a separate antenna, unless there is a group of programs that have very similar levels

it is recommended to use one- or two-channel spacing (e.g. 50, 52, 54, 56, 58 or 51, 54 etc.), unless the number of distributed programs is larger than possible in such an allocation. Without a channel spacing there is a risk of interferences coming from the neighboring channels, especially in older TV sets that are not so selective as the modern televisions. The unfavorable phenomenon can be reduced by especially careful signal leveling in the network;

Illustration of channel spacing

the best choice is band outlets (separation of FM and TV signals) - broadband solutions are characterized by larger attenuation and low separation;

all outputs of network devices have to be closed with terminating resistors, including last outlets in pass-through networks (unless there are used dedicated terminating outlets)

all inputs of the devices used have to be closed, especially when the output signal is the sum of the signals from the inputs (e.g. inputs of an amplifier). As an exception, when the unused inputs are equipped with dedicated gain adjustment, it may be enough to set the gain to a minimum;

using a number of antenna preamplifiers, it is needed to ensure proper supplying voltage (12VDC or 24VDC) and current output of the power supply;

in the case of large networks with long cables it is recommended to use channel converters to avoid distribution of programs in the channels used by terrestrial TV transmitters;

antennas and the masts have to be very well grounded, the same applies to amplifiers, taps, and splitters;

it is recommended to set the level of FM broadcasts ca 10dB lower than TV channels;

calculations are indispensable for achieving good quality of distribution network;

if the network distributes more than two programs, every doubling of the number of programs forces us to decrease output level by 3dB, unless there is another recommendation in the user's manual of the amplifier

it should be avoided to distribute programs in the pairs of channels given below:

Table 3. Unrecommended pairs of channels/bands (1)

Interfering channel/band

1

2

FM

6

7

8

Interfered TV channel

4

5

3

10

11

12

If it is necessary to distribute programs in the pairs of channels given in Table 3, the separation between close receivers has to be over 54 dB, and in the case of channels listed in Table 4 - over 50 dB.

Community antenna (MATV system) may be defined as antenna installation where compensation of network attenuation is performed by one (central) set of amplifiers. The amplifiers can be connected in a cascade.

Unlike MATV, cable TV system compensates network attenuation through a number of section amplifier sets, deployed in different parts of the network. Another feature of large cable installations is a multi-layer (tree) structure.

Community antenna (MATV system) - method of receiving and distributing FM and TV signals in apartment houses, condominiums, and public utilities.

Signal power level (also: signal level or level) - the ratio of signal power to the reference level, expressed in decibels (dB). The power reference level 0 dBmV means the power dissipated in 75 ohm resistance when signal of 1mV voltage is applied to. Signal level is then the ratio of the applied voltage to the reference 1mV (across standardized 75 ohm resistance).

So the actual signal level can be determined as:

P=20logU

where: U - the voltage at 75 ohm load in mV.

The level of FM radio signal is defined as rms voltage of the carrier frequency, of TV signal - rms voltage of the video carrier frequency in peaks of synchronization pulses.

Maximum output level - maximum level of the signal in the output (each output - in case there is more than one) of active device with rated load, limited by intermodulation distortions.

Kinds of MATV systems:

with one amplification stage

with two amplification stages

MATV system with one amplification stage - antenna installation up to 200 outlets, based on one amplifier or set of amplifiers - built in small or medium buildings.

MATV system with two amplification stages connected in cascade - antenna installation up to 1000 outlets, based on cascade of two amplifiers (or two sets of amplifiers) that are situated in a considerable distance one from another. This kind of installation is used in large buildings or in the case of groups of buildings e.g. in a condominium.

Topologies of MATV systems:

star topology (active and passive elements located in a small number of nodal points) - from small- (10-15 outlets) to medium-size installations (100-200 outlets), guarantying small differences of signal levels among outlets;

line topology - not used these days, with 100-200 outlets, no possibility of using program packages. The old installations often used outlets with resistors, and their frequency range was limited to 230 MHz or 606 MHz

hybrid topologies - they combine two or more topologies - used in large systems.

Classification of amplifiers used in MATV systems:

- according to frequency ranges:

channel amplifier - amplifies one TV channel or the FM band

band amplifier - amplifies one TV band

multi-band amplifier - amplifies two or more TV bands

broadband amplifier - amplifies at least two TV bands and has continuous frequency characteristics within the bands

- according to gain control:

no gain adjustment

manual gain adjustment

automatic gain control (AGC)

- according to location in the network:

input amplifier (or preamplifier)

line/end amplifier

- according to powering:

local powering

remote powering (usually via the signal line)

Classification of terminal/subscriber outlets based on application in specific kind of distribution network:

pass-through outlet - characterized by high tap-off attenuation, used as intermediate element in vertical line section

terminal outlet - characterized by high tap-off attenuation, used as the last element in the series in vertical line section, equipped with terminating resistor

low-loss terminal outlet (no loop) - characterized by low attenuation, used e.g. at the end of line in star-shaped network.

Channel conversion - shift of the original channel to any suitable one, e.g. from 28 to 10.

Application:

the way of escaping from channels occupied by terrestrial TV transmitters, which lowers interferences and reflections in the network

the way of utilizing low channels - the only available in older installations - within I, II, III (and sometimes IV) TV bands

in SMATV systems - change of frequency of programs from the first satellite IF (signals from LNB to sat receiver: 950 MHz - 2150 MHz) in order to organize the structure of received channels, as well as to eliminate possibility of collision (the same frequency) of programs from different satellites and polarizations in one-cable installation built without multiswitches.

Channel conversion allows for:

grouping some programs in order to form program packets (solution used in bigger networks or cable TV systems offering various sets of programs for different prices). Usually the basic set includes terrestrial broadcasts;

increasing maximum range of the network through use of lower channels

AM radio programs are not distributed in cable installations, unless some of them are converted (from AM into FM modulation, and shifted into FM band). That's why the networks are capable of providing return channel (below 50 MHz) for data transmission.

Channel conversion

Sources:

PN 79/T-05210 Community antenna installations. General requirements and examination methods.

PKNMiJ Warsaw 1980

Annex No. 21 to directive of Minister of Communications from October 4, 1997: Technical specifications of components used in cable TV; Warsaw 1997